1. Field of the Invention
The present invention relates to methods and apparatus for transmitting analog and digital information signals within a particular frequency bandwidth.
2. Description of the Background
Television broadcasters transmit standard analog television signals over channels regulated by the Federal Communications Commission (FCC). These signals conform to the requirements of the National Television Standards Committee (NTSC), administered by the FCC, and the signals are thus referred to as NTSC analog television signals. The current NTSC standard requires transmission of 525 lines of resolution transmitted as 30 interlaced frames per second (60 half frames per second). The FCC permits transmission of NTSC analog television signals over channels having a 25 megahertz bandwidth, an industry standard.
Recently, broadcasters have had a need to transmit digital television signals with the advent of high definition television (HDTV) and standard definition television (SDTV). These digital television signals are known as HDTV signals and SDTV signals, both of which conform to known industry standards. Obtaining additional bandwidth to transmit digital television signals can be difficult. Expanding a standard 25 megahertz channel is not be possible, at least since another channel likely exists adjacent the channel, and expansion of one channel would cause interference with another. Also, due to a limited number of channels available in the radio frequency (RF) spectrum used for transmission of television signals, broadcasters may have difficulty obtaining additional channels.
Therefore, a technique has been developed to transmit both analog and digital television signals within a standard 25 megahertz channel. This technology involves digitizing an NTSC analog television signal, combining it with an HDTV signal, and transmitting both as one digital signal centered on a carrier signal. However, digitizing an NTSC analog television signal often adversely affects its picture quality, resulting in what are referred to as xe2x80x9cartifactsxe2x80x9d in the picture. In addition, digitizing NTSC analog television signals tends to adversely affect picture quality in panning, involving moving the camera at least horizontally to record an event such as often occurs in recording sporting events.
Furthermore NTSC analog television signals have precise timing requirements that can be difficult to maintain when digitizing the signals. The timing requirements avoid, for example, delays or overlap between program broadcasts, commercials, and a broadcaster""s identifying logo, all of which may arrive from different sources and thus must be precisely timed to generate a continuous uninterrupted picture. As a result, the technology required to digitize NTSC analog signals and combine them with HDTV signals can require a significant amount of processing capability and expensive components.
Accordingly, a need exists for transmitting analog television or information signals with digital television or information signals in the same bandwidth without significantly affecting the picture quality of the analog television signals.
A first method consistent with the present invention transmits combined analog and digital information signals. The method includes receiving an analog information signal and a digital information signal. The analog and digital information signals are combined for transmission within a particular frequency bandwidth while maintaining the analog information signal in analog form.
A second method consistent with the present invention transmits combined analog and digital information signals. The method includes receiving an analog information signal and a digital information signal. The analog and digital information signals are combined for transmission within a particular frequency bandwidth using a first carrier signal for the analog information signal and using a second carrier signal for the digital information signal.
A third method consistent with the present invention receives combined analog and digital information signals. The method includes receiving a signal, transmitted within a particular frequency bandwidth, having a first portion including an analog information signal maintained in analog form and having a second portion including a digital information signal. The analog information signal is separated from the digital information signal.
A fourth method consistent with the present invention receives combined analog and digital information signals. The method includes receiving a signal, transmitted within a particular frequency bandwidth, having a first portion including an analog information signal transmitted using a first carrier signal and having a second portion including a digital information signal transmitted using a second carrier signal. The analog information signal is separated from the digital information signal.
A first apparatus consistent with the present invention transmits combined analog and digital information signals. A first terminal receives an analog information signal, and a second terminal receives a digital information signal. A transmitter, coupled to the first and second terminals combines the analog information signal and the digital information signal for transmission within a particular frequency bandwidth while maintaining the analog information signal in analog form.
A second apparatus consistent with the present invention receives a combined analog and digital information signal. A terminal receives a signal, transmitted within an particular frequency bandwidth, having a first portion including an analog information signal maintained in analog form and having a second portion including a digital information signal. A receiver, coupled to the terminal, separates the analog information signal from the digital information signal.
A third apparatus consistent with the present invention transmits combined analog and digital information signals. A first terminal receives an analog information signal, and a second terminal receives a digital information signal. A transmitter, coupled to the first and second terminals, combines the analog information signal and the digital information signal for transmission within a particular frequency bandwidth using a first carrier signal for the analog information signal and using a second carrier signal for the digital information signal.
A fourth apparatus consistent with the present invention receives combined analog and digital information signals. A terminal receives a signal, transmitted within a particular frequency bandwidth, having a first portion including an analog information signal transmitted using a first carrier signal and having a second portion including a digital information signal transmitted using a second carrier signal. A receiver, coupled to the terminal, separates the analog information signal from the digital information signal.
Another system for providing a common transport signal comprising an analog information signal and a digital information signal, the system also including a transmitter for the common transport signal. The transmitter includes an analog information signal modulator, placing the analog information signal onto a first intermediate frequency, a digital information signal modulator, placing a digital information signal onto a second intermediate frequency, a first upconverter and amplifier for upconverting the analog information signal, and a second upconverter for upconverting a frequency translated digital information signal. The system also includes a power combiner for adding the upconverted analog information and the upconverted digital information signal to form a common transport signal.
The system also provides a means for reception of the common transport signal. The receiver includes a signal receptor and conditioner, a signal splitter and dual signal recovery chains; each chain including at least a downconverter, a bandpass filter and intermediate frequency amplifier, and a signal demodulator.
Another method of transmitting combined analog and digital information signals, includes receiving an analog information signal receiving a digital information signal shifting the frequency spectrum of the analog information signal a first amount, shifting the frequency spectrum of the digital information signal a second amount, and combining the frequency shifted analog information signal and the frequency shifted digital information signal for transmission within a standard television channel bandwidth such that the analog information signal is maintained in analog form during the combining step.
Another method of receiving a combined analog and digital information signal, the method including receiving a combined analog and digital information signal, splitting the combined signal to produce two such combined signals, downconverting the analog information signal by a first amount, downconverting the digital information signal by a second amount, frequency translating the frequency shifted digital information signal, and demodulating the analog information signal and the digital information signal.